An elevator installation is installed in a building. It substantially comprises an elevator cage which is connected by way of support means with a counterweight or with a second elevator cage. By means of a drive, which selectably acts on the support means or directly on the elevator cage or the counterweight, the elevator cage is moved along substantially vertical guide rails. The elevator installation is used for transporting persons and goods within the building over single or multiple stories. The elevator installation includes devices in order to help ensure safety of the elevator installation. A device of that kind protects, for example in the case of stopping at a story of the building, the elevator cage from unintended drifting away. For that purpose use is made of, for example, braking devices which, when required, can brake the elevator cage.
A device of that kind is known from WO 2005/066058. The device consists of a clamping device which in the case of standstill of the elevator cage clamps a moved part, a movement sensor system which detects movement of the clamping device and a control device which evaluates the movement and actuates a safety device if required.